The present invention relates to stretchable conveyor belts, usually of reinforced elastomer construction and which commonly have a troughed conveying reach that defines an upwardly opening, longitudinally extending concavity.
Prior belts of this type have employed centrally-located, inextensible tension elements such as cables to transmit the required driving tension, and pleats or flutes molded in the edges of the belt which fold or unfold as required to accommodate elongation or shortening of the belt edges as it passes through horizontal turns. Such prior belts have been subject to various disadvantages. For example, the flutes in such belts increase the cost of the mold in which the belt is formed as well as the quantity of material used in manufacturing the belt. Material conveyed by the belt will tend to stick in the grooves between adjacent flutes and will drop out when the belt is inverted on its return run to cause excessive carry-back or spillage. Additionally, belt idlers running on the flutes are a source of noise and excess wear, and when the belt runs over a terminal drum or pulley the flutes must elongate excessively. These excess elongations in the flutes are about twice the average belt edge elongation and result in early fatigue failures of the belt material.
U.S. Pat. No. 4,061,223 discloses a belt conveyor system in which a troughed conveyor belt intended to negotiate horizontal turns is provided with reinforcing members extending transversely of the belt and spaced apart longitudinally of the belt. Resilient, deformable material is provided between the reinforcing members to permit stretching of the belt upon installation thereof such that the belt edges remain in tension when the belt passes around curves. The transverse reinforcements help to maintain the molded shape of the belt in such curves. This belt also exhibits certain disadvantages. For example, the belt requires a separate drive element disclosed as a drive or power belt which contacts the conveyor belt to transmit driving tension thereto. As the belt is stretchable an indeterminate amount, it is not possible to apply pulling or driving tension thereto at a single point without further stretching the belt. Such additional stretching is uncontrolled and may vary depending upon physical dimensions of the belt, the material load on the belt and the properties of the material from which the belt is formed. Thus, this belt may not be driven by conventional conveyor belt drives, nor may it be installed on conventional supports as it relies on variable spacing between the terminal pulleys to provide the desired belt stretching.